This invention is a device for preventing unauthorized opening of the doors of a cargo container of the type used on truck trailers or on storage or construction containers. Such containers customarily have two doors hinged to laterally opposite sides of the rear of the container on vertical axes and the doors are latched in their closed position by vertical stanchions mounted on the outside of the doors. The stanchions have latching fingers at their tops and bottoms which engage keeper pockets at the top and bottom of the rear of the container when the stanchions are pivoted about their axes. The trailer bodies or containers are also designed such that the left door is typically closed and secured first and opened last. The right door is designed with a seal around the periphery of the door and its size is such that when closed, the right door retains the left door in a secure position. Consequently, the right door is typically the first door opened and the last closed. Although various locking devices have been proposed for the handles provided for rotating the stanchions, thieves using bolt cutters, power hack saws and sledgehammers are all too frequently destroying the locking devices.